1. Field of the Invention
The present invention relates to an overload protection for rotatable power tools and, in particular, for portable core drilling machines or power tools for concrete.
2. Description of the Prior Art
During core drilling in concrete with annular core bits formed of a hard material and having a diameter greater than 100 mm, high press-on forces and torques, which are usually generated during core drilling, lead to very high loads acting on the power tools the dimensions of which, based on a required power, are limited because of the portability requirements. Therefore, these power tools require a good overload protection to prevent damage of the power tools, in particular, the damage of their electromotor and torque-transmitting gears.
German Publication DE-41 19 941 discloses a portable power tool in which for protection of the annular core bit-driving electric motor, the current and temperature are monitored with control electronics which, if needed, cut the power supply from the electric motor by actuating a power switch.
German Publication DE-31 28 410 discloses a power tool in which the acting torque is monitored by control electronics which, in case of overload, cuts off the drive train from the electronic motor by operating a magnetic clutch.
An object of the present invention is to provide an overload protection arrangement for a portable power tool and which while being dimensioned for high press-on forces and torques, occupies relatively small space.